Method of heat treatment of coal

ABSTRACT

The proposed method is characterized by raising the temperature of heating of a coal charge in each subsequent stage by a value which is somewhat less than the temperature rise in the preceding stage so that in the next to last stage there is provided heating of the coal charge to a temperature at which the resin vapours start to isolate from the coal charge. The method is also characterized in that the circulating gaseous heat carrier of the nest to last and the last stages of heating is purified from impurities prior to the recirculation. In order to carry this method into effect, the multistage apparatus is provided with a chamber for purification of the gaseous heat carrier from impurities arranged between two groups of chambers for successive step-wise heating of the coal charge.

Skornyakov et a1.

[ METHOD OF HEAT TREATMENT OF COAL [76] Inventors: Jury Pavlovich Skornyakov, ulitsa Ekonomicheskaya, 7a, kv. 33; Jury Borisovich Tjutjunnikov, ulitsa Kostomarovskaya, 5/7, kv. 10; Anatoly Semenovich Petrukhno, ploschad R. Ljuxemburg, 5, kv. 26; Filipp Savelievich Schelkunov, prospekt Gagarina, 20, kv. 72, all of Kharkov, USSR.

[22] Filed: Nov. 6, 1970 [21] Appl. N0.: 87,398

[52] U.S. Cl 201/27, 201/9, 201/29, 201/44, 202/150, 202/114 [51] Int. Cl Cl0b 49/00 [58] Field of Search 201/26, 27, 9, 29, 32, 201/43, 44; 202/117, 150, 134, 113, 114; 34/79-82, 76-78, 73; 48/210 [56] References Cited UNITED STATES PATENTS 2,626,234 1/1953 Barr et a1 201/44 X CHAMBER FOR OXIDATION OF TAR VAPORS FIRST COAL- HEATING STAGE |O-I85C CIRCULATION BLOWER 5 7 V GAS PIPLINE Sept. 17, 1974 Steinschlaeger 201/29 Angevine 201/44 X [5 7] ABSTRACT The proposed method is characterized by raising the temperature of heating of a coal charge in each subsequent stage by a value which is somewhat less than the temperature rise in the preceding stage so that in the next to last stage there is provided heating of the coal charge to a temperature at which the resin vapours start to isolate from the coal charge. The method is also characterized in that the circulating gaseous heat carrier of the nest to last and the last stages of heating is purified from impurities prior to the recirculation. In order to carry this method into effect, the multistage apparatus is provided with a chamber for purification of the gaseous heat carrier from impurities arranged between two groups of chambers for successive step-wise heating of the coal charge.

4 Claims, 1 Drawing Figure FOURTH COAL-HEATING STAGE 380440C SECOND COAL-HEATING STAGE I85 310C -I J 4 COAL PASSING LINE THIRD COAL-HEATING STAGE HEATCARRIER GENERATOR\ METHOD OF HEAT TREATMENT OF COAL The present invention relates to the coke and chemical industry and, more particularly, this invention relates to methods of heat treatment of coal, preferably low-metamorphisated gas coal, that is, coking coals with a high volatile content, and to multistage apparatus for effecting this method.

The invention can be effectively used for production of moulded blast-furnace coke.

Known in the art are multistage apparatus for heat treatment of disintegrated coal or a coal charge by a gaseous heat carrier which provides for several stages of heating of the coal charge and comprises heating chambers disposed in series along the charge flow and connected to each other through coal ducts and also connected to each other and to a heat carrier generator through gas ducts, said apparatus being equipped with a circulating pump for feeding a portion of the exhaust heat carrier into the generator.

The heat treatment of coal in these apparatus is effected through heating the coal charge by the circulating gaseous heat carrier fed from the generator successively into each heating stage towards the flow of coal which is heated in the last stage to a plastic state.

However, on effecting such a method, the last heating stage, as viewed along the coal flow, is under the greatest heat load and this results in liberation of an in creased amount of resin vapours from the coal charge so that the small-size coal grains completely lose their caking capacity. The resin vapours isolated from the coal at a temperature of conversion thereof into a plastic state are transferred by the flow of the heat carrier through all components of the apparatus and form coal resin deposits in coal and gas ducts which disrupt their normal operation. In order to remove these deposits, it is necessary to stop the whole apparatus.

An object of the present invention is to eliminate the above mentioned disadvantages.

The main object of the invention is to develop such a method of heat treatment of coal and such a multistage apparatus for carrying this method into effect which will provide for transformation of the coal into a plastic state, while eliminating the isolation of an increased amount of resin vapours from the coal being treated and the pollution of the heat carrier.

This object is accomplished through such a method of heat treatment of coal, particularly lowmetamorphisated gas coal, which provides for a successive step-wise heating of the coal charge by a circulating gaseous heat carrier, in which, according to the invention, the temperature in each subsequent stage is raised to a value somewhat less than the temperature rise in the preceding stage so as to provide for a heating of the coal charge in the next to last stage to a temperature of initial liberation of resin vapours, in which case the circulating gaseous heat carrier of the last stage and of the next to last stage in the direction of movement of the charge is purified from impurities prior to the recirculation.

ln this case the heating of the coal in the next to last stage to a temperature providing for the beginning of isolation of resin vapours therefrom makes it possible to reduce the heat load of the last stage and to transmit to the coal in the last stage only that amount of heat which is required for the completion of the thermochemical processes.

In such operating conditions the basic amount of heat is transmitted to the coal in the first heating stage so that the possibility of overheating of the coal in the last stage and deterioration of its baking capacity is reduced.

As compared with the known method of heating, the loss of the baking capacity of the coal consisting of particles less 0.25 mm in diameter, which is most sensitive to the conditions of heat treatment, is reduced by a factor of 12 to 14.

It is expedient to heat the coal charge in the next to last stage to a temperature of 350-400C. Heating the charge in this manner more than two times reduces the loss of the resin vapours from the coal.

The above-said object is accomplished most effectively if the gaseous heat carrier is purified from the impurities by adding air thereto in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume.

In connection with the proposed method, an apparatus is provided which is intended for heat treatment of coal.

The apparatus is preferably provided with chambers for successive step-wise heating which, according to the invention, are arranged in two groups disposed along the flow of heat carrier, and a chamber for purification of the gaseous heat carrier from impurities being located between these groups.

Such disposition of the chamber for freeing the gaseous heat carrier from impurities provides for an increase in reliability and operational stability of the apparatus as a whole due to oxidation of the resin vapours and prevention of formation of coal-resin deposits in coal and gas ducts. In this case the efficiency of the apparatus is increased by a factor of 3 to 3.5. The utilization of heat is increased by 10-12 percent, while fuel consumption is reduced due to the use of the heat obtained in the process of oxidation of the resin vapours and the coal dust.

Other specific objects and advantages of the invention will be better understood upon consideration of some embodiments thereof with reference to the accompanying drawing illustrating a block diagram of a multistage plant for heat treatment of coal according to the invention.

The multistage apparatus for efiecting the proposed method of heat treatment of coal is shown in the drawing wherein the temperatures shown correspond to the conditions of Example 1. The apparatus provides for four heating stages comprising four chambers l, 2, 3 and 4 for successive step-wise heating of a coal charge interconnected through a coal duct 5 and, according to the invention, a chamber 6 for purification of a gaseous heat carrier by means of oxidation of the impurities occuring in this carrier, which chamber 6 has an air inlet 7 and a fuel inlet 8. The chamber 6 is located between the two groups of the chambers l, 2, 3, 4 arranged along the flow of the heat carrier and communicating through a gas duct 9 with each other and with a heat carrier generator 10 having an air inlet 11 and a fuel inlet 12 and also with a circulating pump 13.

The apparatus operates as follows:

The starting material in the form of disintegrated coal charge is fed through the coal duct 5 into the first heating stage the chamber 1 and then is successively fed through the chambers 2, 3, 4 in each of which the charge is heated to a higher temperature until the completely treated coal charge is removed from the chamber 4 for further treatment such as moulding of blast furnace coke.

According to the invention, in each successive heating stage the temperature is increased by a value somewhat less than the temperature rise in the preceding stage so as to provide heating of the coal charge in the next to last stage to a temperature at which the resin vapours start to separate from the charge.

The gaseous heat carrier is produced in the generator by burning a fuel in a mixture with air and diluting the products of combustion with the exhaust heat carrier fed by the circulating pump 13 until a required temperature is obtained. From the generator 10 the fresh heat carrier is simultaneously fed into the chambers 3 and 4, i.e., into the next to last and the last stages for heating the coal charge preheated in the chambers I and 2. The heat carrier removed from the chambers 3 and 4 is fed, according to the invention, into the chamber 6 for oxidation of the resin vapours occurring in this carrier. This chamber is also fed with air and fuel. One portion of the air introduced into the chamber 6 in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume is used for oxidation of the resin vapours, whereas the other portion is used for combustion of the fuel to effect continuous initiation of the oxidation of the resin vapours. The heat carrier purified from the resin vapours is fed from the chamber 6 simultaneously into the chambers l and 2 for preheating the coal charge. The excessive portion of the exhaust heat carrier is removed from the apparatus through removing it from the chamber 1 of the first heating stage. The other portion of the same together with the exhaust heat carrier leaving the chamber 2 of the second heating stage is drawn by the pump 13 which then forces the exhaust heat carrier into the generator 10 for diluting the products of combustion.

Distribution and control of the flows of the heat carrier are effected by means of adjustable gates (not shown) mounted on the gas ducts.

Example 1 The apparatus is used for heat treatment of lowmetamorphisated gas coal disintegrated to a content of 92-95 percent of the groups with particle size less than 3 mm, having a moisture content of 8.3 percent and a baking capacity of 15-16 Rogs units. The temperature of the beginning of intensive isolation of resin vapours from this coal is within the range of 370-380C, while the temperature of transformation of this coal into a plastic state is equal to 435440C. In the first heating stage, i.e., in the chamber 1, the coal is heated from a temperature of 10C to a temperature of 185C during 9.3 see. by the heat carrier fed from the chamber 6 for oxidation of the resin vapours. The coal fed from the chamber 1 is heated in the second stage, i.e., chamber 2, from 185 to 310C during 8.2 sec.

From the chamber 1 the excessive portion of the exhaust heat carrier is removed from the apparatus, whereas the other portion together with the exhaust heat carrier from the chamber 2 is fed through the circulating pump 13 into the generator 10 for diluting the products of combustion.

in the chamber 3, which is the next to last stage of heating in the apparatus, the coal is heated to 310C during 8.3 sec. and then is heated to a temperature of 380C which is the temperature of beginning of isolation of resin vapours (or close to it) which is determined by the known analytical method of the gas release dynamics at a corresponding heating rate.

From the chamber 3 or the third heating stage the coal is fed into the chamber 4 which is the last heating stage. In this stage the coal is brought to a plastic state by heating it to 440C during 7.9 sec. After that the thermally treated coal is removed from the chamber 4 and is directed for further treatment.

in this case the baking capacity of the coal having a particle size less than 0.25 mm and being most sensitive to the conditions of the heat treatment was reduced only to 10-11 units, whereas in the case of the treatment by the known method it was reduced to 1.0-0.8 unit according to the Rogs method.

The basic amount of the resin vapours penetrates into the heat carrier in the last stage, i.e., in the chamber 4. In the mass-production conditions, however, at occasional fluctuations of temperature some amount of resin vapours can also be present in the next to last stage, i.e., in the chamber 3. To prevent this, the exhaust heat carrier from the third and fourth chambers, before using it for recirculation, is directed into the chamber 6 for purification by means of oxidation of the resin vapours. In this case air is added to the heat carrier in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume.

The temperature rise of the coal in the first stage of heating is equal to 175C, in the second stage is equal to C and in the third stage is equal to 60C.

Thus, in the proposed operating conditions of heat treatment of coal the basic amount of heat is given to the coal in the first heating stages having the lowest temperature and, due this fact, it is possible to avoid overheating of the coal and deterioration of its baking capacity.

Example 2 The apparatus is used for treatment of a mixture of two grades of coal: 70 percent of coal of class 6, group 3, division 3 and 30 percent of low-baking coal of class 3, group 1, division 3 (according to the international classification of coals) disintegrated to the content of 94-95 percent of the classes with a particle size less than 3 mm and a moisture content of 10.8 percent. The temperature of the beginning of isolation of resin vapours from this mixture of coals is equal to 365375C while the temperature of transformation into a plastic state is equal to 445-455C.

1n the first heating stage, i.e., the chamber 1, the coal is heated from 10 to C during 9.3 see. by the heat carrier fed from the chamber 6 for oxidation of the resin vapours. The coal fed from the chamber 1 is heated in the second stage, i.e., chamber 2, from 170 to 315C during 8.2 sec.

From the chamber 1 the excessive portion of the exhaust heat carrier is removed from the apparatus while the other portion together with the exhaust heat carrier from the chamber 2 is forced by the pump 13 into the generator 10 for diluting the products of combustion.

In the chamber 3, which is the next to last stage of heating, the coal is heated from 315 to 400C during 8.3 sec. This temperature is a temperature of the beginning of isolation of resin vapours (or close to it) which is determined by the known analytical method by the gas release dynamics at a corresponding heating ratev From the chamber 3, which is the third heating stage, the coal is fed into the chamber 4 serving as the last heating stage wherein the coal is brought to a plastic state by heating it to a temperature of 450C during 7.9 sec. Then the thermally treated coal is removed from the chamber 4 and is directed for moulding of blast furnace coke.

In this case the baking capacity of the coal having particle size less than 025 mm was reduced to 9-10 units while in the case of heat treatment by the known method it was reduced to l.00.8 units according to the Rogs method.

The exhaust heat carrier from the third and fourth chambers, prior to the recirculation, is directed in the chamber 6 for freeing it from impurities by means of oxidation. For this purpose air is added to the heat carrier in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume.

The temperature rise of the coal in the first stage is equal to 160C, in the second stage 145C, in the third stage 35C and in the fourth stage 50C.

Therefore, in the proposed conditions of heat treatment of coal the basic amount of heat is brought thereto in the first stages of heating and this makes it possible to eliminate overheating of the coal and deterioration of its baking capacity.

We claim:

1. A method of heat treatment of lowmetamorphisated coal, which comprises effecting successive step-wise heating of a coal charge by a circulating gaseous heat carrier, in each subsequent stage of heating the temperature being raised by a value somewhat lower than the temperature rise in the preceding stage so as to provide heating of said coal charge in the next to last stage by said gaseous heat carrier to a temperature wherein resin vapours are initially liberated from the charge, said gaseous heat carrier removed from the next to last and the last stages of heating, as viewed along the direction of movement of the coal charge, being purified from impurities, and recirculating said carrier.

2. A method according to claim 1 in which the coal charge in the next to last stage is heated to a temperature of 350400C.

3. A method according to claim 1 in which the gaseous heat carrier is purified from impurities in a purification chamber at high temperatures by means of adding air to the heat carrier in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume.

4. A multistage apparatus for heat treatment of lowmetamorphisated gas coal, by means of successive stepwise heating of a coal charge by a circulating gaseous heat carrier comprising: a plurality of chambers for successive step-wise heating of the coal charge by said circulating gaseous heat carrier arranged in two groups located along the flow of the heat carrier, a coal duct interconnecting said heating chambers, a chamber for purification of said gaseous heat carrier from impurities brought thereto in the next to last and the last stages of heating the coal charge located between said groups of the heating chambers, a generator for said gaseous heat carrier, a circulating pump for said heat carrier, a gas duct connecting said generator and said circulating pump to each other and to said groups of the heating chambers and also connecting said groups of the heating chambers to each other through said chamber for purification of the heat carrier. 

2. A method according to claim 1 in which the coal charge in the next to last stage is heated to a temperature of 350*-400*C.
 3. A method according to claim 1 in which the gaseous heat carrier is purified from impurities in a purification chamber at high temperatures by means of adding air to the heat carrier in the amount corresponding to the content of free oxygen in the purified heat carrier up to 3 percent by volume.
 4. A multistage apparatus for heat treatment of low-metamorphisated gas coal, by means of successive step-wise heating of a coal charge by a circulating gaseous heat carrier comprising: a plurality of chambers for successive step-wise heating of the coal charge by said circulating gaseous heat carrier arranged in two groups located along the flow of the heat carrier, a coal duct interconnecting said heating chambers, a chamber for purification of said gaseous heat carrier from impurities brought thereto in the next to last and the last stages of heating the coal charge located between said groups of the heating chambers, a generator for said gaseous heat carrier, a circulating pump for said heat carrier, a gas duct connecting said generator and said circulating pump to each other and to said groups of the heating chambers and also connecting said groups of the heating chambers to each other through said chamber for purification of the heat carrier. 